Underweight Horses: Surveillance, Management Considerations

Neglect isn't the only reason horses become underweight. A variety of issues can cause low body weight in horses, including dental problems, parasite infestations, and chronic disease.

Photo: Photos.com

By Grant Miller, DVM-- Reprinted from The Horse Report with permission from the Center for Equine Health, School of Veterinary Medicine, University of California, Davis.

You are driving on a country road and pass a picturesque scene of several horses grazing in an open field. You notice one horse standing away from the group. Without being able to see much detail, it appears to you that this horse does not look like the others. Its ribs are showing and its hip bones are protruding. Like many concerned citizens, you wonder if the horse is okay, and if someone knows that it is underweight. Is anyone doing anything to address this issue? Should you call someone?

General Observations of Underweight Horses

Veterinary involvement in cases is instrumental to a successful outcome.

Cases in which underweight horses have been completely deprived of food for a long period of time (days to weeks) are far more complicated and critical than cases in which the horse has had access to food.

Diarrhea and colitis that occur during refeeding are serious complicating factors that lower the chance for successful rehabilitation.

In some cases underweight horses might display abnormal behavior in relation to eating, such as aggression during feeding time or pica (the ingestion of inappropriate feed such as hair, feces, or dirt/sand/gravel). These psychological conditions might not resolve, despite a return to optimum body condition.

Determining the cause(s) of the poor body condition and adequately addressing them will greatly influence the speed and efficiency of recovery.

Very rarely will a horse not gain weight or reach optimum body condition, provided that the causes of the low body condition can be adequately addressed. An exception would be horses suffering from end-stage organ failure.

The ability of a horse to regain weight can vary widely. Some horses might only take a few weeks to reach an optimum body condition, while others can take many months.

If you have experienced this, you are not alone. Animal control agencies indicate that scenarios like this are reported on a daily basis throughout the United States. Reports of underweight horses are made to local animal control departments, humane societies, or legal authorities. These agencies will, in most cases, conduct a site visit to investigate complaints.

Clearly defined ribs and protruding hip bones seem to be the most common "triggers" that initiate calls to authorities. Other common reports include observations that a horse is not being fed on an ongoing or routine basis, or that there is not enough feed available in the pasture where a horse is housed.

While some reports are credible and warrant investigation and intervention, some are determined to be unfounded. Animal control officers frequently report that complaints about underweight horses are inaccurate or that further investigation uncovers facts about the case that justify the condition of the animal. In some instances, the horse is under veterinary care, while in others the owners have already taken measures to remedy the situation.

It is clear that reports should be addressed on a case-by-case basis, since circumstances surrounding underweight horses can differ greatly in each instance.

So what should you do if you drive by a horse that appears too thin? The most important thing to not do is to leap to conclusions. Making sure that you get an accurate look at the horse is crucial to determining if an action should be taken. In many cases, observing the horse from a different angle (and not at a "split second" glance) can end up resolving initial concerns. Do not trespass to get a closer look but do gather relevant facts such as an accurate description of the animal (color, sex, defining marks, etc.) and a specific geographic location (address or description of the area) and report it to the local animal control authorities.

Common Causes of Low Body Weight Condition

There are a variety of causes for low body weight condition in horses, and these are described below. If you are rehabilitating an underweight horse, particularly a severely underweight horse, it is important to have a veterinarian determine the cause of the condition at the outset, because other medical interventions might be needed in addition to an appropriate feeding regimen.

Inadequate Caloric Intake--Inadequate caloric intake accounts for the majority of underweight horses. In this scenario, energy (in the form of calories) is taken in by ingestion of nutrients (hay, pellets, grain, etc.) in order to meet the metabolic demands of the body. But if the caloric expenditure put out by the body to meet metabolic demands (such as staying warm during cold weather, pregnancy, lactation, etc.) exceeds caloric intake, the body will turn to body stores for energy. Thus, as body tissues (fat and muscle) are dissolved for energy, the body loses weight.

There are two general scenarios that occur in which a lack of adequate caloric intake is the cause of suboptimal body condition. In one scenario, the horse lives for an extended period of time without any ingested feed. Again, it is highly advisable to contact a veterinarian before giving the horse feed because feeding can induce diarrhea and colitis (inflammation of the colon), which can both be life-threatening to horses. Diarrhea can cause irreparable dehydration and electrolyte imbalances. Colitis can lead to endotoxemia and sepsis (blood-borne infection), which can cause nearly instantaneous death. Horses can also become laminitic as a consequence of colitis.

In the second scenario, the horse has feed but its net caloric intake is inadequate. This can occur when a horse is being fed a suboptimal amount of food, is not being fed appropriate feeds, or is only being fed on a sporadic basis. In some situations, the horse is being fed a good amount of food on a regular basis, but the food is inappropriate for that horse (for example, poor quality hay with low nutritive value, pregnant horse that requires extra food, or horse that is missing several teeth and cannot chew hay).

It should be noted that both of the scenarios above can occur if a horse is housed with herd mates that are dominant. In such a scenario, herd dynamics can result in one horse not consuming adequate feed, even when ample feed is provided. Therefore, some horses might need to be isolated from more dominant herd mates during feeding, or be moved to a different location so that they do not have to compete for food.

When inadequate caloric intake is determined to be a cause of low body condition, an appropriate feeding regimen should be formulated for the horse. In general, the following tips might be useful when formulating a feeding plan to assist an underweight horse in gaining weight:

Veterinary consultation and oversight is advised early in the rehabilitation process.

Small, frequent meals on a 24-hour basis can help horses through the more critical stages of rehabilitation (usually during the first two to four weeks of refeeding).

High-quality feed sources are beneficial. When possible, low carbohydrate, calorically dense feed that is high in digestible energy should be provided.

A clean, fresh water source in the form of a large bucket is useful because water intake can be monitored.

Appropriate feedstuffs (i.e., feeds that the horse can chew and digest) are recommended. Examples of recommendations include: pelleted/soaked feeds for horses with dental issues, senior pellets for some cases, low carbohydrate/high digestible energy hay such as alfalfa for other cases.

Avoid the "one-size-fits-all" approach to refeeding. Each feeding program is dynamic and can require adjustments on an ongoing basis depending on how the horse responds.

The use of gastroprotectants such as omeprazole (marketed as Gastrogard or Ulcergard) can be beneficial in some cases. The use of probiotics with yeast can be useful in some cases, however they might not be warranted in all cases. The use of digestive aids should be carried out with the advice of a veterinarian.

Avoid other stressors such as a loud environment or an inconsistent feeding schedule.

Use blankets and provide shelter to help the horse keep warm (lower energy expenditure) during inclement weather or cold environments to aid in increasing body weight.

Dental Issues--Dental problems in horses can contribute to weight loss, although it is very rare to find a horse that is underweight due solely to dental problems. Usually dental problems will contribute to low body condition score in combination with inadequate caloric intake. Because equine teeth (hypsodonts) grow throughout the animal's life, chewing over time creates sharp enamel points on the upper outside and lower inside edges of the premolars and molars (cheek teeth). These sharp points can dig into the cheeks and gums, making it painful for a horse to chew.

In addition, missing teeth, fractured teeth, or malocclusion such as parrot mouth can impair a horse's ability to adequately grind food when chewing. Horses with pain from dental problems can drop food ("quid") or only partially chew food before swallowing it. Because chewing is the first step in digestion, food that has not been adequately chewed and ground down into smaller bits will pass through the body whole. If it is not ground down to a size in which the body can digest it for energy use, food can end up being inefficiently utilized. Thus, weight loss can occur because the body must use its own stores to use as fuel to meet metabolic demands.

Addressing dental problems can increase the efficiency by which the body can absorb nutrients and energy from food. It is recommended that the horse have its teeth examined and floated (filed) to correct sharp enamel points and any other occlusion issues. Dental care should be performed by a veterinarian.

Infection and Infestation--If a body has to expend extra energy as a result of an ongoing infection or parasite infestation, weight loss can sometimes occur. In some circumstances, horses feel sick as a result of an infection or infestation and thus will not eat even though adequate food may be available. Examples of chronic infection include pneumonia, pyometra (uterine infection in mares), peritonitis (inflammation of the membrane lining the abdomen), and internal abscesses. If a horse cannot eat enough to meet the metabolic need of the disease in addition to other energy needs (like staying warm, working, etc.), weight loss will result.

A physical exam performed by a veterinarian during the early stages of case management can greatly alter the outcome of a rehabilitation case. The exam can help illuminate signs of chronic infection or parasite infestation. In many cases, blood testing can also help determine if and where an infection is occurring. A fecal McMasters test is an essential test to determine whether or not parasites may be playing a role in poor body condition score. The McMasters test quantifies the number of parasite eggs present in a fecal sample. This is important because the mere presence of parasite eggs does not necessarily mean that parasites are contributing to weight loss. In actuality, the number of eggs present helps to determine whether or not they are a factor. Fecal samples must be fresh in order for results to be accurate.

In each equine case of infection or parasitism, medication and management practices will vary.

Organ failure like heart, liver, and kidney can also all result in profound loss of body condition. Each of these diseases has their own mechanism by which they result in an increased metabolic demand, but they all draw on a body's energy stores. In some circumstances, horses feel sick as a result of their disease and thus will not eat, despite having plenty of food available. In other cases, the metabolic demand placed on the body by the disease or condition exceeds the energy intake of the horse, thus creating a negative energy balance and subsequent weight loss.

Each medical condition involves its own diagnosis, testing, medical treatment, and management considerations. For these reasons, it is essential that underweight horses be examined by a veterinarian in the early stages of their rehabilitative process.

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